Vapor chamber having integral captive fasteners

ABSTRACT

A vapor chamber for spreading heat includes a housing having spaced-apart first and second plates, the first and second plates defining a hollow chamber. At least one opening is defined through the first and second plates, the opening being isolated from the hollow chamber. At least one insert is fitted into each opening. The insert may be a snap-in insert or may be stamped into the opening.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to heat spreaders, and morespecifically to a heat spreader having a vapor chamber.

[0003] 2. Description of Related Art

[0004] As integrated circuit chips decrease in size and increase inpower, the heat sinks required to maintain a desired temperature havegrown to have a much larger footprint than the chips. Heat sinks aremost effective when there is a uniform heat flux applied over the entireheat input surface. When a heat sink with a large heat input surface isattached to a heat source with a much smaller contact area, there issignificant resistance to the flow of heat to the other portions of theheat sink which are not in direct contact with the integrated circuitchip. Higher power and smaller heat sources, or heat sources which areoffset from the center of the heat sink, increase the resistance to heatflow to the balance of the heat sink. This phenomenon can cause greatdifferences in the heat transfer rate from various parts of the heatsink. The effect of this unbalanced heat transfer is reduced performanceof the integrated circuit chip and decreased reliability due to highoperating temperatures.

[0005] Conventional approaches to handling the increased heat flux fromthe heat source include increasing the size of the heat sink, increasingthe thickness of the heat sink surface which contacts the device to becooled, increasing the air flow which cools the heat sink, and/orreducing the temperature of the cooling air. However, these approachesincrease weight, noise, system complexity, and expense.

[0006] Currently, an advantageous mechanism for overcoming theresistance to heat flow in a heat sink is to attach a vapor chamber to abase of the heat sink, such as in the Therma-Base™ heat spreadermanufactured by Thermacore, Inc. of Lancaster, Pa. This vapor chamber isa vacuum vessel with a saturated wick structure lining the inside walls.As heat is applied to the base of the vapor chamber, the working fluidat that location vaporizes. Wherever the vapor comes into contact with acooler wall surface it will condense, releasing its latent heat ofvaporization. The condensed fluid returns to the heat source viacapillary action in the wick structure. As in a heat pipe, the thermalresistance associated with the vapor spreading is negligible, providingan effective means of spreading the heat from a concentrated source to alarge surface.

[0007]FIG. 1 shows a prior art assembly comprising a vapor-chamber-typeheat spreader 10 and a finned heat sink 20. The heat sink 20 is acold-forged or machined heat sink having fins 22 attached to a baseplate 24. The base plate 24 and heat spreader 10 have openings 30therethrough to receive fasteners 40 for fastening the heat spreader 10and heat sink 20 to a heat generating device (not shown). The openings30 through the vapor chamber 10 are formed in depressions 32 cast in oneof the plates 12 of the vapor chamber 10 so that the vapor chamber 10remains a sealed evacuated envelope. An insert 50, such as a PEM insert,is stamped into the openings 30 of the base plate 24. The inserts 50receive and retain the fasteners 40.

[0008] In the Therma-Base™ heat sink assembly, the heat spreader 10 isattached to a base 24 of the finned heat sink 20 by soldering, adhesionbonding, brazing or the like. Through-holes 30 are provided through theheat spreader 10 and base 24 for insertion of fasteners 40 for mountingthe heat sink 20 to the heat input source. The base is typically a solidconductive metal, such as aluminum, for example. Inserts 50 forcaptively holding the fasteners are mounted to the base 24 of the finnedheat sink 20. The base 20 must be cold forged or machined, and addsweight and volume to the system.

[0009] An improved mounting structure for a heat sink with avapor-chamber-type heat spreader is desired.

SUMMARY OF THE INVENTION

[0010] The present invention is a heat spreader comprising a housinghaving first and second plates defining a hollow chamber therebetween.At least one opening is defined through each of said first and secondplates of the housing. The housing has a surface defining at least onepassage connecting the openings of the first and second plates. Thepassage is isolated from the chamber. At least one insert is adapted forreceiving a fastener. The at least one insert is mounted directly intothe at least one passage.

[0011] Another aspect of the invention is a heat spreader comprising ahousing including first and second plates that define a hollow vaporchamber therebetween. At least one depression is formed in one of theplates which projects into the vapor chamber and is bonded to the otherof the plates. The housing has an opening that penetrates through thedepression and the other of the plates. An insert is adapted to receivea fastener. The insert is mounted directly into the opening.

[0012] Another aspect of the invention is a heat sink comprising: ahousing including first and second plates with an enclosed vapor chambertherebetween. At least one depression is formed in one of the plateswhich projects into the vapor chamber and is bonded to the other of theplates. The depression has an opening defined therethrough, so as todefine an isolated passage through the vapor chamber. An insert isdirectly mounted into the opening and shaped to receive a fastener. Atleast one fin is attached to the one of the plates of the housing.

[0013] Another aspect of the invention is a method for forming a heatspreader comprising the steps of: joining first and second plates todefine a hollow vapor chamber therebetween; forming at least onedepression in one of the plates, so that the depression projects intothe vapor chamber and is bonded to the other of the plates; penetratingthe depression and the other of the plates; and mounting an insertdirectly into the opening, said insert being adapted to receive afastener.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other objects, features and advantages of the presentinvention will be more fully disclosed in, or rendered obvious by, thefollowing detailed description of the preferred embodiment of theinvention, which is to be considered together with the accompanyingdrawings wherein like numbers refer to like parts and further wherein:

[0015]FIG. 1 is a cross-sectional view of a prior art heat sinkassembly.

[0016]FIG. 2 is a cross-sectional view of one embodiment of the presentinvention showing a snap-in insert.

[0017]FIG. 3 is a cross-sectional view of another embodiment of thepresent invention showing a stamped-in insert.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] Referring to FIG. 2, an exemplary heat sink 101 according to oneembodiment of the present invention comprises a heat spreader 100enclosing a vapor chamber 130 and including an insert 170, and a captivefastener 300. The heat sink assembly 101 may have one or more fins 200attached directly to the housing 110, 120 of the heat spreader 100.

[0019] The heat spreader 100 of the exemplary embodiment comprises afirst plate 110 and a second plate 120 defining a hollow chamber 130therebetween. Heat spreader 100 has a wick structure (not shown)preferably on both plates, and a working fluid (not shown). At least oneopening 160 is defined through the vapor chamber 100, as explainedbelow, and at least one insert 170 is mounted directly into eachrespective opening 160.

[0020] The first plate 110 and second plate 120 have inside surfaces 112and 122, respectively, outside surfaces 114 and 124, respectively, andperipheral lips 116 and 126, respectively. The bottom (first) plate 110has at least one depression 118 formed therein. Alternatively, thedepressions may be formed in the top (second) plate 120. The first plate110 and second plate 120 are spaced apart and sealed at their peripherallips 116 and 126 defining a hollow chamber 130 between the plates.

[0021] Referring again to FIG. 2, the heat spreader 100 is assembled inthe following manner. The inside surfaces 112 and 122 of the first andsecond plates are covered with a wick structure (not shown), such as asintered metal capillary wick. The first plate 110 and second plate 120are sealed together at their peripheral lips 116 and 126 by, forexample, welding, brazing or soldering or the like. The vapor chamber130 is evacuated to remove all non-condensible gases. A suitablequantity of working fluid is placed within the vapor chamber 130, toform a functioning vapor chamber two phase heat spreader.

[0022] Depressions or dimples 118 which project into the vapor chamber130 of heat spreader 100 are formed in the first plate 110. Thedepressions 118 are formed and dimensioned so that when first plate 110and second plate 120 are joined, the surfaces contact and can be joinedto form a gas or leak tight seal, resulting in a through hole in thevapor chamber heat sink 100. The passage defined by the surface of thedepression 118 connects the holes in the first and second plates 110,120. Because the openings or passages 160 within the depressions 118 areisolated from the vapor chamber 100, the vacuum integrity of the vaporchamber 100 is not compromised. The edges 119 of the depressions 118 ofthe first plate 110 around the openings 160 remain sealed to the insidesurface 122 of the second plate 120. In addition to providing a meansfor forming openings 160 in the vapor chamber 100, the depressions 118also assure that the spacing between the first plate 110 and secondplate 120 are maintained, even where pressure differentials between theinside volume of the vapor chamber 100 and surrounding environment mightotherwise cause the plates 110 and 120 to deflect toward each other. Thedepressions 118, which essentially form columns within the vapor chamber130, prevent the plates 110, 120 from bowing inward, and thereforemaintain the flat surface 114 for contact with the heat source, such asan integrated circuit chip (not shown).

[0023] Although openings 160 have been described as being formed throughdepressions 118, it should be understood that such openings could beformed in the housing of heat spreader 100 in other ways. For example,the heat spreader 100 could be pre-formed with hollow columns or spacersbetween the first and second plates.

[0024] In one embodiment of the invention, as shown in FIG. 2, a snap-inplastic insert 170 is mounted directly into the openings 160 in thevapor chamber 100, without mounting the insert to a base plate of a heatsink. The insert 170 is adapted to receive captive fasteners 300. Thesnap-in plastic inserts 170 may be specially designed and formed to fitthe openings 160 through the heat spreader 100 or alternatively, theopenings 160 may be formed to fit commercially available off-the-shelfplastic snap-in inserts 170. Because these inserts 170 are flared at thebottom, they are self-retaining. Thus, the insert does not require anoversized diameter or an interference fit with the portion of opening160 having the narrowest diameter. The number of depressions 118 andopenings 160 through the heat spreader 100 may vary depending on thenumber of fasteners 300 desired for attachment of the heat spreader 100to the heat generating source (not shown). The heat source abuts theoutside surface 114 of the first plate 110.

[0025] In another variation of the device of FIG. 2, the plastic insert170 may be of an anchor type that is sized to be smaller in diameterthan opening 160 before the fastener 300 is inserted, and flares out tograsp the opening when the fastener 300 is inserted.

[0026] According to another embodiment of a heat sink 201, as shown inFIG. 3, an insert 190, such as a PEM broaching nut insert (Manufacturedby Penn Engineering and Manufacturing Corp., of Danboro, Pa.), isstamped into the openings 160, which are under-sized to provide a tightinterference fit. In order to form the structure required for the insert190, the first plate 110 has excess material at the location of thedepressions 218 to provide extra strength to withstand the stamping ofthe insert 190. The extra material is provided by using a plate that isthicker in the surface 218 of the opening than in the remainder of theplate 110.

[0027] In addition to the through holes provided in the depressions 118(or 218) or columns, the vapor chamber 130 may also include spacers,which may be solid and which extend between and contact the first andsecond plates of the housing. These spacers (not shown) also prevent theplates from bowing inward, and therefore assist in maintaining the vitalflat surface for contact with the heat generating source.

[0028] Referring again to FIGS. 2 and 3, according to another aspect ofthe exemplary embodiments, a folded fin 200 may be directly attached tothe outside surface 124 of the second plate 120 of the heat spreader 100by soldering, adhesion bonding, brazing, or the like. The folded fin 200includes openings 210 aligned with the openings 160 of the heat spreader100 to allow for the receipt of the fasteners 300. Fasteners 300 areinserted into the openings 210 of the folded fin 200 and the inserts 170in the embodiment of FIG. 2 (or 190 in the embodiment of FIG. 3) of theheat spreader 100. The fasteners 300 secure the heat sink assembly 101to the heat generating source. The type of fasteners may vary dependingon particular application for which the heat sink assembly is beingused.

[0029] The folded fin 200 is formed from a single folded metal sheetwhich is preferably made of copper or aluminum. By folding the fins overthemselves, the folded fin assembly provides a large surface area in asmall space. Folded fin technology maximizes surface area and minimizespressure drop, thus increasing the flow of heat from the heat generatingsource to the air. Preferably, the folded fin has an open top design toallow for air flow. Also preferably, the folded fin has a maximum finheight of about 10 cm (4 inches), a maximum fin flow length of about 61cm (24 inches), a minimum fin thickness of about 0.005 cm (0.002inches), a maximum fin thickness of about 0.1 cm (0.040 inches), aminimum fin density of about 0.8 fins per cm (2 fins per inch) and amaximum fin density of about 32 fins per cm (80 fins per inch).

[0030] The folded fin does not include the base structure contained inthe typical cold-forged or machined heat sink. Thus, the use of a foldedfin reduces the weight and volume of the heat transfer assembly. Thisreduced weight and volume simplifies and speeds the design cycle and caneliminate the need for complex bracing required for heavier heattransfer assemblies having finned heat sinks with base structures.

[0031] Although the use of a folded fin 200 is preferred, otherconventional fin configurations may be used.

[0032] The heat spreader 100 and fin configuration 200 of the heat sinkassembly 101 will have various features and dimensions depending on theapplication. In an exemplary embodiment to be used for transferring heataway from an integrated circuit device, the vapor chamber may beapproximately 7.6 cm (3.0 inches) by 8.9 cm (3.5 inches) with a totalthickness of 0.5 cm (0.200 inch). First plate 110 and second plate 120may be constructed of OFHC copper 0.08 cm (0.035 inch) thick, anddepressions 118 may span the 0.25 cm (0.100 inch) height of the internalvolume of the vapor chamber 130. The wick structure (not shown) may beconstructed of sintered copper powder and may average 0.1 cm (0.040inch) thick. The depressions 118 may have about a 0.63 cm (0.250 inch)outer diameter, and openings 160 may be approximately 0.53 cm (0.210inches) in diameter.

[0033] Although the invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

What is claimed is:
 1. A heat spreader comprising: a housing havingfirst and second plates defining a hollow chamber therebetween, at leastone opening defined through each of said first and second plates of saidhousing, said housing having a surface defining at least one passageconnecting the openings of the first and second plates, wherein saidpassage is isolated from said chamber, and at least one insert adaptedfor receiving a fastener, the at least one insert being mounted directlyinto said at least one passage.
 2. A heat spreader comprising: a housingincluding first and second plates that define a hollow vapor chambertherebetween; at least one depression formed in one of said plates whichprojects into said vapor chamber and is bonded to the other of saidplates; said housing having an opening that penetrates through saiddepression and the other of said plates; and an insert adapted toreceive a fastener, wherein said insert is mounted directly into saidopening.
 3. The heat spreader of claim 2, wherein the insert snaps intosaid opening.
 4. The heat spreader of claim 3, wherein the insert iscomprised of plastic.
 5. The heat spreader of claim 2, furthercomprising a captive fastener held within the insert.
 6. The heatspreader of claim 2, wherein the insert is stamped into said opening. 7.The heat spreader of claim 6, wherein a thickness of said first orsecond plate is greater in the at least one depression than thethickness of said first or second plate remote from the at least onedepression.
 8. The heat spreader of claim 2, wherein said first andsecond plates each include a peripheral lip located at an edge of saidhousing, said peripheral lips bonded together.
 9. The heat spreader ofclaim 2, wherein said at least one depression comprises a flat surfacethat is in contact with an inner surface of said other of said plates.10. The heat spreader of claim 2, wherein each of said plates includesan interior confronting surface and a peripheral lip located at an edgethereof, said peripheral lips being bonded together so as to define thevapor chamber.
 11. The heat spreader of claim 2, wherein said depressioncomprises an annular inner surface of said first plate that is bonded toa corresponding annular edge surface in said second plate.
 12. A heatsink comprising: a housing including first and second plates with anenclosed vapor chamber therebetween; at least one depression formed inone of said plates which projects into said vapor chamber and is bondedto the other of said plates; said depression having an opening definedtherethrough, so as to define an isolated passage through said vaporchamber; an insert directly mounted into said opening and shaped toreceive a fastener; and at least one fin directly attached to one of theplates of said housing.
 13. The heat sink of claim 12, wherein the finis a folded fin.
 14. The heat sink of claim 13, wherein the insert snapsinto said opening.
 15. The heat sink of claim 14, wherein the insert iscomprised of plastic.
 16. The heat sink of claim 12, further comprisinga fastener held within the insert.
 17. The heat sink of claim 12,wherein the insert is stamped into said opening.
 18. A method forforming a heat spreader comprising the steps of: joining first andsecond plates to define a hollow vapor chamber therebetween; forming atleast one depression in one of said plates, so that the depressionprojects into said vapor chamber and is bonded to the other of saidplates; penetrating said depression and the other of said plates to forman passage through the vapor chamber; and mounting an insert directlyinto said opening, said insert being adapted to receive a fastener. 19.The method of claim 18, further comprising attaching at least one findirectly to the other of said plates.
 20. The method of claim 18,further comprising inserting a fastener into said insert.